The present invention relates generally to the field of intraluminal support devices, or stents. More particularly, the present invention relates to self-expanding and balloon expandable stents having a ring structure architecture.
Various types of disease conditions present clinical situations in which a vessel of a patient needs to be artificially supported to maintain an open passageway through which fluids, such as blood, can flow. For example, blood flow through an artery can be impeded due to a build-up of cholesterol on the interior wall of the vessel. Also, vessel walls can be weakened be a variety of conditions, such as aneurysms.
Intraluminal support frames, sometimes referred to as stents, provide an artificial mechanism to support a body vessel. Stents are typically tubular-shaped members that are placed in the lumen of the vessel and, once deployed, exert a radially-outward directed force onto the vessel wall to provide the desired support.
Stents are typically positioned at the point of treatment by navigation through the vessel, and possibly other connected vessels, until the point of treatment is reached. This navigation requires the stent to be able to move axially through the vessel(s) prior to deployment, while still maintaining the ability to exert an outward force on the interior wall once deployed. Accordingly, stents typically have radially collapsed and expanded states. In the collapsed state, the stent has a relatively small diameter that allows it to move axially through the vessel. In the expanded state, the stent has a relatively large diameter that allows it to exert an outward force on the interior wall of the lumen, thereby providing the desired support to the vessel. During navigation through the vessel(s), the collapsed stent will likely encounter various turns and bends. Therefore, it is desirable for the collapsed stent to exhibit at least a minimum degree of axial flexibility along the longitudinal length of the stent.
Many stents longitudinally contract while radially expanding, thereby affecting the size of the body vessel that is treated or affected by the stent. As a result of this longitudinal contraction, medical professionals may insert into a patient a stent having a collapsed length that is longer than the length of the portion of the body vessel that is to be treated, thereby potentially increasing the difficulty of advancing the stent through the various turns and bends leading to the treated area. Therefore, it is desirable to minimize longitudinal contraction of the stent during radial expansion.
Stents are often formed by removing material from a cannula, such as a piece of tubing, so that the cannula becomes expandable. The size and strength of a particular stent is typically related to the size of the piece of tubing from which the stent is formed. For example, a stent formed from a larger piece of tubing will generally exhibit a greater radial strength than a stent formed from a smaller piece of tubing. However, a stent formed from smaller piece of tubing will generally have a smaller collapsed state diameter than a stent formed from a larger piece of tubing.
It is therefore desirable to provide a stent having a sufficient radial strength in its expanded state and a sufficiently small diameter in its collapsed state, while exhibiting a minimum degree axial flexibility along the longitudinal length thereof and while maintaining a generally constant length while radially expanded from the collapsed state to the expanded state.